A wind turbine rotor blade comprises an airfoil shape over much of its length, and usually has a circular root end for connecting to a circular pitch bearing on the wind turbine hub. A rotor blade is generally manufactured by arranging layers of fibre material in two blade halves, and joining these blade halves together. Root bushings are embedded in the root end, so that fasteners such as bolts can be used later on to mount the rotor blade to the hub. Resin infusion can be performed in a vacuum-assisted resin transfer moulding (VARTM) step to obtain a structurally sound and relatively light blade. In a manufacturing process in which the blade halves are joined before performing resin infusion, it is critical to ensure that an accurate arrangement of the root bushings, so that the rotor blade can later be mounted to a pitch bearing of a wind turbine hub. To this end, a mounting ring can be used to assist in ensuring that the root end meets the required manufacturing tolerances. Such a mounting ring can be temporarily connected to some or all of the root bushings in order to hold them in place while the blade is being completed. The root bushings can be connected to the mounting ring, and the entire assembly can be lowered into a blade half. However, a circular or one-piece mounting ring is associated with added complexity in the process of arranging fibre material between the root bushings mounted on the ring.
One approach can be to manufacture the mounting ring as two ring segments or ring halves. The first ring segment is arranged in one mould half, and the second ring segment is placed in the other mould half. After completion of a fibre layup step, and arranging fibre material between the root bushings, one mould half is turned and lowered onto the other mould half so that the mould can be closed for the subsequent infusion and curing steps. One problem with this solution is that placement of the ring halves need to be performed very accurately, otherwise compression or shifting of the fibre material may result when the blade mould halves are joined, since the mounting ring halves may push or compress the fibre material.
Furthermore, it may be difficult to accurately align the two mounting ring halves when the blade moulds are joined together. Even a small misalignment between the two mounting ring halves or a slight offset of a ring half is highly undesirable. If the two ring halves are not exactly aligned and planar when the first and second mould halves are joined, the result can be a defective root end, so that the entire rotor blade may be useless. For this reason, the conventional mounting ring halves are associated with relatively high level of effort to ensure accuracy during manufacture of the mounting ring halves, during placement of the mounting ring halves in the mould, during the blade mould joining steps, etc. Therefore, the conventional mounting ring halves are also associated with correspondingly high manufacturing costs.